2. Getting started

31 03 2013

Marine chronometers don’t like being moved around. This may seem to be a strange statement to make about instruments that spent their working lives on bridges of ships at sea, so it needs some explanation. When the balance wheel is oscillating back and forth it is unconnected with the rest of the chronometer for most of the time and it is only when it is releasing a tooth of the escape wheel or receiving a push (“impulse”) from it via the escapement that the two are connected. If the instrument is suddenly rotated at the wrong time, two teeth of the escape wheel may be released instead of one (“tripping”) or the impulse jewel may be struck amiss or the detent damaged (you can read  in the book about how these parts work). The main message of this paragraph is that moving a chronometer around needs care. It is particularly vulnerable to damage if it is fully run down, so it should be moved when it is at least partially wound, as this keeps the escape wheel locked in the correct position. If it is to be transported it should be partially wound and the balance wedged unless it is going to make only a short trip in your hands or resting on your knees. When carrying it from one place to another move deliberately and avoid sudden rotational movements as, for example, when turning to close a door behind you.

How to wind a chronometer may seem to be a mystery. No key or keyhole is visible on the front, and on the back, there is a hole, but it seems to have a dead end. Let us start, however, with the key. A chronometer must not be wound clockwise (nor should the hands ever be turned backwards) so it is provided with a key called a tipsy key that will only allow anti-clockwise rotation Figure 1). If it is turned clockwise, a clutch should slip, so begin your acquaintance with the instrument by checking that this does indeed happen when you hold the stem of the key and turn the handle clockwise: sometimes the clutch mechanism gets clogged with dirt or rust.

Figure 1 : A Tipsy key.

Figure 1 : A Tipsy key.

Does the chronometer need to be wound? There is an indicator at the 12 o’clock position that shows how long the chronometer has run since being wound. Usually, fully wound is shown at zero on the right, but it varies a little from maker to maker. Figure 2 shows a fully down Russian MX6 chronometer.

Figure 2 ; Fully run down.

Figure 2 ; Fully run down.

The key hole is on the back, so the gimbal lock has to be released (Figure 3) and the chronometer turned over sideways about the 12 to 6 o’clock axis (Figure 4). The key hole seems to have a blind ending, but if you rotate the cover clockwise, the winding stem will be revealed.

Figure 3 : Unlocking the gimbals.

Figure 3 : Unlocking the gimbals.

Figure 4 : Dust cover and key hole revealed.

Figure 4 : Dust cover and key hole revealed.

You now have to insert the tipsy key and wind it anti-clockwise slowly and steadily (Figure 5). To fully wind a 2- day chronometer, that is to say the vast majority, takes seventeen and a half  half-turns. Twenty four hours run takes seven and a half half-turns and it is worth counting so that you don’t run hard up against the stop-work that prevents overwinding.

Figure 5 : Winding the chronometer

Figure 5 : Winding the chronometer

The winding indicator should then indicate zero (Figure 6). Remove the key and let the dust cover rotate backwards under the control of a finger, as chronometers don’t like sudden mechanical shocks any more than they like rotations.

Figure 6 : Chronometer fully wound.

Figure 6 : Chronometer fully wound.

You can at this point return the instrument to a face up position, but do it handsomely, which is old sailor-speak for “carefully, gently.” Captain Lecky in his famous book “Wrinkles in Practical Navigation,” described how a sailor of his acquaintance returned the chronometer face up by rotating in end for end instead of side to side (Figure 7) and then had no idea how to get it facing the right way again.  I leave this as an exercise for the reader…

Figure 6 : Duh!

Figure 7: Duh!

Once you have the instrument facing the right way, lock the gimbals and leave them locked at all times except when it is on board a vessel. To start the chronometer, rotate it sharply one way through about 30 degrees while face up. This should start it if it is in good order and the balance not corked.

A corked balance is unrelated to corked wine though the source of the cork may be a wine bottle. “In the beginning” describes how to open up the case and Figure 8 shows a cork wedge being inserted (or removed) from a balance.

Figure 7 ; Corking (or uncorking) a balance.

Figure 8 ; Corking (or uncorking) a balance.

The unpractised or heavy handed are better steadying the balance with a fine artist’s camel hair brush rather than with a gloved hand as shown, but if you have a light and delicate touch and are confident that you will not shear off the balance pivots or disturb the timing weights, by all means use a gloved finger, bearing in mind that confidence is the feeling you get when you have failed fully to understand a complex matter. Note that the wedges go directly under the balance arms and are inserted just far enough to arrest movement without dropping out. When removing them, pull them straight out in line with the balance arms.

If you have wound the clock and uncorked the balance, you can use the artist’s brush to rotate the balance to see if it will start. You can also use it gently to stop the balance when necessary.





1. In the beginning…

31 03 2013

Just to be clear, this blog is mainly about the marine chronometer, sometimes called a box chronometer. Some of them were made for use in the air and for use by surveyors, but usually do not differ fundamentally from the basic marine chronometer. I will not be writing about what is nowadays often called a chronometer: a mechanical wrist watch made to standards that meet the requirements of certain Swiss manufacturers’ bodies, nor will I be including what is properly called a  chronograph : a  watch with a stop watch function. However, I will cover a certain class of large watches designed for navigation, as I come across them.

There is very little difference between various makers and you can recognise a marine chronometer because it is in the form of a mechanical (as opposed to quartz) clock that sits in a heavy case face up in gimbals in a fine wooden case with a glass top. A clock is essentially a clockwork motor that is permitted to run down step by equal step by some sort of vibrating mechanism, a pendulum or balance wheel, that in return receives a little energy from the motor to keep it vibrating. The intermediate part that takes care of this exchange is called the escapement and it is this (and the quality of manufacture) that mainly distinguishes the chronometer from a common clock, as it has ben devised to interfere as little as possible with the balance wheel (makers soon learned that a pendulum clock was useless at sea).

Supposing you find a chronometer or are offered one for sale. How do you tell whether it is worth buying? A useful question to ask is “Does it go?” If answered in the negative, it may be because a former owner has carefully prepared it for storage by wedging the balance wheel so that it cannot vibrate and be damaged by careless handling. Hamilton Model 21 chronometers mostly have a special mechanism to do this. It may be that someone has attempted to wind it clockwise with the key provided and found that it just turns round and round without anything happening inside or it may be that it has been wound anticlockwise (correctly) and that nothing has happened on completing the wind. This is because chronometers, unlike lever clocks and watches, are not self starting.

If it does not go, ask the owner if you may wind it and try to start it by giving a brisk turn through about thirty degrees with the face up. If this starts it and the second hand moves half a second at a time with two ticks, a loud one and a much softer one per half second, you have a running chronometer. If it jumps through full seconds, or ticks irregularly you still have  a running instrument but one that needs attention and that should be stopped as soon as you can.

If you cannot start it, (assuming that it is not a Hamilton Mod.21, which will need another post) ask if you may look inside. To do this, you will have to remove it from its gimbals. Tilt the gimbal ring forward so that the 12 is uppermost and rotate the case through 90 degrees. This will allow you to loosen a circular locknut and remove a large screw that acts as a pivot at the top of the ring (Figure 1) and you can then lift the chronometer off the other pivot and manoeuvre it out of the box. You can enlarge the photos by clicking on them, returning to normal by using the back arrow at top left.

Figure 1 : Removing the chronometer from the gimbals

Figure 1 : Removing the chronometer from the gimbals

It is best at this point for you to be wearing close-fitting light rubber gloves to avoid marring the internal finish of the instrument by sweat or dirt. Unscrew the heavy glass top and place it aside and then invert the movement into the fingers of one hand placed around the perihpery of the dial, well away from the hands. With any luck it will fall out of the case on to your fingers (Figure 2) and you can then place it back into its case face downwards. There is a little peg at 12 o-clock that fits into a slot in the edge of the case.

Figure 2 : Removing movement from case.

Figure 2 : Removing movement from case.

Most chronometers will look something like in Figure 3, unless it is an Ulysse-Nardin or Hamilton Mod 21, when it may look something like in Figure 4. In the latter’s case, you can see the Y-shaped locking fork.  The balance is the ring shaped thing with a helical spring in its centre.

Figure 3 : Movement out if the case.

Figure 3 : Movement out if the case.

Figure 4: Hamilton Model 21.

Figure 4: Hamilton Model 21.

If there are slips of cork underneath the balance, ask the owner if s/he would remove them (carefully, using tweezers) and then try again to see if the instrument will start. If it will not and it is fully wound, you are faced with a bill to overhaul it of US$250 at the least and probably quite a lot more if there is a broken part to be renewed or repaired. This may be well worth while and add value to a chronometer dating from before 1940 and you may well feel that you would like to own a nineteenth  century chronometer, whatever its condition. If it is a mess of rust and verdigris it is probably best left with its present owner unless offered at a price that cannot be refused.

“The Mariner’s Chronometer” will take you safely through the overhaul of most chronometers, which show remarkably little variation between makers from about 1840 onwards, but of course, you embark on this  at your own risk. I well remember that it took me a few days to pluck up the courage to  start an overhaul that at the end of the day may have converted a going instrument, worth perhaps US$2000 on a good day, into an expensive ornament. However, there are really only three delicate components that require more than ordinary care: the balance staff, the detent and the escape wheel. Buy the book and learn more about them. If you have pots of money and bags of time, entrust it to someone with experience of chronometers (a diminishing bunch) and ask if you may watch him or her at work.